The retinal pigment epithelium (RPE) is an integral component of the blood-retinal barrier and as such helps maintain the appropriate environment for normal retinal function. Derangements of RPE blood-retinal barrier function have been associated with clinical disease. The long term goal of our research is to fully characterize the transepithelial transport properties of the RPE and to examine the ways in which the RPE functions as a barrier to the passive diffusion of many substances. The specific aims of this proposal are: to further develop our in vitro rabbit RPE-choroid preparation. To use this preparation: to employ pharmacologic agents with known effects on other transport systems, to manipulate the extracellular ionic mileu of the RPE, to perform isotope flux studies, and to make measurements of trans-RPE fluid movements by employing our newly developed photogrammetric apparatus in order to develop a model of mammalian RPE transepithelial transport and barrier function. The effects of long term retinal detachment on RPE transepithelial transport and barrier function will be assessed by repeating selected experiments in rabbits with long standing retinal detachments.